1. Field of the Invention
The invention relates to the use of known copolymers, based on polysiloxanes, as emulsifiers for the preparation of W/O (water/oil) emulsions, whose oily phase consists of or contains silicone oil.
2. Description of the Prior Art
For the preparation of emulsions of the W/O type, emulsifiers are used which preferably are soluble or dispersible in oil and whose HLB value generally is less than 8. Such emulsifiers are normally used in an amount of 10 to 20 weight percent, based on the weight of the oily phase. Examples of such W/O emulsifiers include the fatty acid esters of glycerin, polyglycerin, sorbitol or wool wax alcohols. As the fatty acid component, oleic acid or isostearic acid is generally used.
These W/O emulsions are preferred for use in cosmetics and pharmacy, but are also used for technical purposes.
According to the state of the art, special difficulties arise in the preparation of water/oil emulsions whose oily phase consists partly or completely of silicone oil. Conventional emulsifiers based on polyol esters of fatty acids do not produce satisfactory emulsions with silicone oils. Special formulations have to be worked out in each case for particular problems.
For example, U.S. Pat. No. 4,268,499, page 1, line 6, discloses antiperspirant preparations in the form of W/O emulsions which consist of:
(a) 30-60 parts by weight of an aqueous solution of an astringent, e.g., aluminum chloride, as a discontinuous phase; PA0 (b) 27-67.5 parts by weight of a volatile liquid with a boiling point below 250.degree. C., e.g., a cyclic dimethylsiloxane; PA0 (c) 0.5-3 parts by weight of a W/O emulsifier with an HLB value of 2 to 10; PA0 (d) 1-5 parts by weight polyoxyalkylene-polysiloxane copolymer; and PA0 (e) 1-5 parts by weight of an O/W emulsifier with an HLB value of 11 to 17;
wherein components (a) to (e) add up to 100 parts by weight.
Furthermore, for the preparation of W/O emulsions whose oily phase consists of silicone oil or contains this oil in a predominant amount, emulsifiers are commercially obtainable which consist of a solution of polyoxyalkylene-polysiloxane copolymers in a cyclic siloxane. These products are obtainable, for example, under the name of DOW CORNING Q2-3225C. Their use is described in the brochure "A Formulary of Product Application in Skin Care by DOW CORNING".
These products are, however, not satisfactory in all respects. The W/O preparations must be storage stable in order to ensure an adequate shelf life and a constant product quality. The emulsions must maintain a constant consistency over a period of several months, and neither oil nor water may separate out. This storage stability must, moreover be maintained at temperatures ranging from -5.degree. C. to +40.degree. C. There are, however, still particular difficulties with preparing stable W/O emulsions having silicone oils as the oily, continuous phase, wherein the silicone content is higher than 20 weight percent and preferably, higher than 30 weight percent, based on the total weight of the emulsion, and/or which contain, in addition to the silicone oil, other oily substances, such as, paraffin oils, ester oils or liquid or solid waxes, such as, vegetable, animal or mineral waxes. The W/O emulsions prepared from such mixtures of silicone oil and carbon-based organic oils using emulsifiers of the state of the art, generally show inadequate emulsion stability and break within hours or days. Even the preparation of a briefly stable emulsion is frequently impossible.
Copolymers are known in which polyoxyalkylene groups, as well as long-chain hydrocarbon groups are linked to a linear polysiloxane. The synthesis of such compounds is described in U.S. Pat. Nos. 3,234,252, 4,047,958, 4,427,958, 3,427,271 and 2,846,458. The synthesis is preferably accomplished by adding an olefin with, for example, 6 to 18 carbon atoms, and a polyoxyalkylene ether of an olefinically unsaturated alcohol, e.g., the polyoxyalkylene ether of allyl alcohol, to a polydiorganosiloxane having SiH groups, the addition being carried out in the presence of a catalyst containing platinum.
According to U.S. Pat. No. 4,381,241, these copolymers can be used as emulsifiers for the preparation of W/O emulsion of salt solutions in liquid hydrocarbons, which can be used as drilling liquids. There is no indication, however, that such compounds could be suitable for the preparation of W/O emulsions, the oily phase of which consists of silicone oil and, optionally, of other carbon-based organic oils or waxes.